There are known in the prior art masks for use by persons working in contaminated or polluted atmospheres. Usually these masks cover both the nose and mouth of the wearer and by one expedient or another permit him to breath while working in the contaminated or polluted atmosphere without harm.
It is often desirable that a person wearing a mask of the type described above be able to communicate with other persons in the same locality, whether they be persons wearing masks and working in the polluted atmosphere, or a person or persons in the same general area but outside the polluted area. With masks of the prior art which are not provided with some built-in communication system, such local external communication is not possible without removing the mask, thus defeating its purpose.
Masks of the type described above, are subject to relatively stringent regulations imposed by various governmental bodies to ensure that persons wearing the masks are fully protected. Any proposed change in the design of an existing mask requires the approval of these regulatory bodies before the change can be incorporated in the mask itself. While such approval is highly desirable for the protection of the person using the mask, it consumes time and results in an expense to the manufacturer proposing the design change.